For many 4k TVs with mediocre brightness rating , they don't nearly have the specs to showcase the dynamic range of HDR content in its full glory .
Therefore when it comes to HDR content mastered at very high nits ( brightness ) , they have to choose to either retain the highlight details or blown out the details to sustain the brightness . This process is called tone mapping .
At this time , there are no standard which define which tone mapping method is right . For the TV makers , Sony's TV tend to go for the brightness while LG is leaning towards keeping the details .
Samsung's TV by nature , will always choose to retain details at the cost of losing brightness of the overall APL .
LG's TV used to be similar but back in 2017 , LG has introduced a different approach to HDR 10 called Dynamic tone mapping ( Active HDR ) which purpose is to adjust the HDR meta data frame by frame .
This can partially restore brightness to the HDR picture , while keeping details intact . Samsung TV on the other hand , doesn't do any dynamic tone mapping .
This might explain why GTS looks brighter on the LG TVs when the specs of both TV are more or less on the same level .
P/S : Samsung's entry level 4K TVs (namely NU7400 , NU7100 , NU7300 , MU6100 , MU6300 etc etc ) have a feature called" UHD Dimming " , which is an algorithm based dimming function that tries to darken the overall picture to improve the contrast . Sadly this come with the cost of dimming down the small and bright highlights. You will want to use every trick from the book to notice a difference from SDR on these TVs , I recommend setting "Contrast Enhancer " to high .
Ah that makes sense. Turning on Contrast Enhancer on the Samsung TV does make it slightly better.